The invention relates to an arrangement for the relief of the piston rod packing of a hydraulic telescopic shock absorber having a cylinder which is divided into two chambers by a piston movable by a piston rod. The lower cylinder chamber is connected by a non-return valve opening in the direction of the cylinder with a reservoir arranged outside of the clyinder to supply damping medium to the cylinder during outgoing piston rod volume. The upper cylinder chamber is closed by a cover or cap in which the piston rod is guided and in which the piston rod packing is arranged. In the space between the piston rod guide and the piston rod packing one or more drain channels are connected for draining damping medium which is leaking along the piston rod guide.
In such prior art shock absorbers the drain channels outlet or drain into the damping medium reservoir which is filled partially with damping fluid and partially with air under atmospheric pressure and in which during normal operation the overall pressure is small even when the piston rod volume driven out of the cylinder is taken up in the reservoir. However, during intensive operation of the shock absorber the temperature thereof may rise substantially due to heat generation in the cylinder and because the air in the reservoir is also heated. Accordingly, the pressure can rise to undesirably high values. This is also caused by the restricted capacity of the reservoir which is dimensioned as small as possible so that the shock absorber can be installed in a restricted space. With the usual proportion of the fluid volume and air volume of 1:1 in the reservoir with a fully loaded shock absorber and when the piston rod is retracted, a temperature rise up to 185.degree. C. has been measured causing an excessive pressure of 4 bar in the whole system. Due to the high friction caused by the high pressure the packing is subjected to premature wear and loses its sealing function.